Cover glass



Jan. 26, 1937*. s. l.. LEBBY v2,068,805

COVER GLASS INVENTOR. 'f/l 716.5 FE 537 A TTORNE YS.

Jan. 26, 1937. l s L, EBBY 2,068,805 I COVER GLASS Filed Feb. 4,1935 '2sheets-sheet 2 IN V EN TOR. 57.475.5/2 549? ATTORNEYS. V

Patented Jan. 26, 1937 UNITED STATES 'COVER' GLASS States Lee Lebby,Corning, N. Y., assignor to Corning Glass Works, Corning, N. Y., acorporation of New York Application February 4, 1935, Serial No. 4,922

4 Claims.

This invention relates to cover glasses, and more particularly to acover glass having certain refractive characteristics that render itespecially adapted for use in signalling.

In signalling equipment, such as railway and trafc signals, it iscustomary to utilize cover glasses placed in front of the lightprojecting System to shield it and also to modify the direction of thebeam of light coming therefrom. Inasmuch as there are times when asignal is lighted and therefore intended to serve as an indication,

and there are other times when it is unlighted and is not intended toserve as an indication, it is necessary that the signal .be such thatthere will be no uncertainty as to Whether it is lighted or not.

In many previous signalsv it has been noticed that when the rays of thesun or the light from an approaching vehicle enter the signal and fallupon portions of' its projecting system, it will appear to be lightedwhen in fact it is not, so that a person approaching the Signal willmisconstrue the state of facts of which thev condition of the 'signal issupposed to be an indication, often with disastrous results. Y

`Such lfalse' signal indications, which are in reality reflexindications and are often referred to as phantom indications, usuallyappear as a small spot of light and,`inasmuch as the close-upindications of previous signals have generally api peared as a, similarspot of light, confusion has often resulted.

It is an object of this invention to produce a new and improved type ofSignal indication.

Another object isto project a primary beamr ofE substantially parallellig'ht of high intensity and a secondary asymmetric beam of light whichin Aone plane spreads through a relatively Wide angle and progressivelydecreases in intensity as the angle from which it is viewed recedes fromthe axis of the main beam while in a plane at right angles to the firstplane, it is spread symmetrically with relation to and slightly inexcess of the main beam with similar ldiminishing intensity.

A further object is to so intermingle the primary andV secondary beamsat their source that the cover glass will always present the appearanceof a filled aspect when viewed from any position within the primaryorsecondary beams.

The above and other objects may be accomplished by employing myinvention which embodies among its features a concavo-convextransparent.plate having distributed over its con'cave surface aplurality oftransparent light cleflecting members, each, having three sides, one ofwhich is contiguous with 'the concave face of the plate while the othertwo sides converge to form a ridge lying along a line which intersectsthe the concave face of the plate at two spaced (ci. rrr-329)' points.One of the faces of each member simply Serves as a riser while the otheronactive face is of cylindrical contour as it recedes from the ridge.

Other features embody the symmetrical distribution of the lightdeflecting members in spaced rows over the concave face of the plate andso proportioning them with relation to the plate that they willintercept only a limited portion of the light projected upon the platewhen it is employed as the cover glass of a projecting system.

In the drawings:

Fig. 1 is a diagrammatic View illustrating the paths of the primary andsecondary beams produced by my cover glass when it is used inconjunction with a traliic signal;

Fig. 2 is a graph upon which is plotted a` curve Showing the varyingintensity inone type of secondary asymmetric beam which my cover glassis capablevof producing;

Fig. 3 is an elevation of the inside of a cover glass embodying myinvention:

Fig. 4 is a vertical transverse section on the line 4-4 of Fig. 3illustrating the cover glass in use with a conventional type of lightprojector;

Fig. 5 is a horizontal transverse section on the line 5 5 of Fig. 3;

Fig. 6 is an enlarged sectional View of a fragment of my improvedA coverglass showing the light deflecting members in detail;

Fig. '7 is an enlarged vertical View similar to Fig. 4 of a fragment ofmy cover glass showinglof the light deflecting members;

Fig. 9 is a view similar to Fig. 8 of a modified form of light deectingmember, and Fig. 10 is a fragmentary sectional view through a coverglass showing the light distribution therethrough when it is equippedwith light derlecting members of the type shown in Fig. 9.

Referring to the drawings in detail, my lmproved cover glass consists ofa transparent plate designated generally I0 having a convex outer face II, a concave inner face I2 of a curvature equal to that ofthe'outerface, and a circumferential flange I3. The plate is preferably of glasspressed to form with light deflecting members to' be more fullyhereinafter described formed integral therewith, though of course insome instances the latter may be separately formed and attached to theplate I0 by a suitable transparent cement.

Distributed symmetrically over the inner concave face I2 of the coverglass and so proportioned with relation thereto as to interrupt but alimited amount of parallel light passing theregenerally I4 which, asshown, are preferably arranged in uniformly spaced` parallel rows withthose in one row staggered with relation to those in the next adjacentrow. This arrangement causes the secondary beam to emanate from thesignal unit from a plurality of uniformly distributed and spacedportions of the cover glass so that when the latter is viewed from anyposition within the secondary beam, it will cooperate with the functionof the eye of an observer known as the persistence of vision so as toproduce the appearance of being illuminated over its entire surface andeffect what is commonly called a filled aspect.

From the fact that approximately seventy-flve or more per cent ofthelight falling upon the cover glass I0 passes directly through aplurality of uniformly distributed surfaces of equal curvature and isunrefracted,.it is evident that the cover glass, when viewed from anyposition within the main beam, will appear in full aspect.

In order to obtain the desired distribution of light intensity in thesecondary beam and to simultaneously secure a symmetrical spread thereofin a plane perpendicular to the plane in which it is deflected, thelight deflecting members each have three sides I5, I6, and II. The sideI5 of each light deecting member is contiguous with the inner face I2 ofthe cover glass I0 and hence is of spherical contour and produces norefraction at its junction with the concave face I2 while the sides I6and I1 converge to form a ridge I8 which lies along a line whichintersects the concave face I2 of the cover glass at two spaced points.The side I 6 of the light deflecting member forms a riser which ispreferably so shaped and positioned with relation to the light passingthrough the cover glass as to produce no refraction nor interferencewith any refracted ray while the side I'I is of cylindrical contour asit recedes from the ridge and conse' quently produces an asymmetricallydeflected beam which, upon emergence through the convex face II of thecover glass, is spread symmetrically to a slight degree in a planeprependicular to the deection produced by the side II of the lightdeflecting member. Due to the fact that the side I'I is cylindrical inform and that the side I 5 is of spherical contour, it becomes evidentthat the active sides I5 and I1 of the light deflecting members I4progressively diminish in area as the ends of the deflecting members areapproached and as a result the long range portions of the secondaryasymmetric beams, i. e., those closest to the axis of the primary beam,will be of greater intensity than those portions further away from theaxis of the primary beam so as to produce a light distribution in thesecondary beam which follows intensities illustrated by the curveplotted in Fig. 2.

As shown in Fig. 4, I illustrate my cover glass in use with aconventional type of light projector for producing a primary beam ofparallel light. In this embodiment the projector consists of aprojection mirror I9 in which a suitable light source, such as anelectric bulb 20, is mounted. The cover glass I0 is shown mounted infront of the open side of the reflector in such a position that thelight deflecting members I4 will interrupt the primary beam at uniformlyspaced intervals and deflect a predetermined limited portion of theprimary beam into an asymmetric secondary beam which spreads through arelatively wide angle in one direction but possesses but limited spreadin a direction at right angles thereto. Obviously other suitable typesof projectors for producing a primary beam of substantially parallellight may be employed without 'in any way departing from the spirit andscope of my invention.

This application is a continuation in part of my forfeited applicationSerial Number 231,140, filed November 4, 1927, and allowed April 4,1934.

I claim:

1. The combination with a cover glass having a convex outer face and aconcave inner face of a plurality of light deflecting members on theinner face of the cover glass, each light deflecting member comprising atransparent body having three sides, one of which is contiguous with theinner face of the cover glass While the other two sides converge andform a ridge which lies along a line which intersects two spaced pointson the concave face of the cover glass, the ridges of the lightdeflecting members being parallel, one of said converging sides of eachlight deecting member being an active face of cylindrical contour as itrecedes from the ridge, the active faces of the light deflecting membersbeing on the same sides of the ridges.

2. The combination with a cover glass having a convex outer face and aconcave inner face of a. plurality of light deflecting members on theinner face of the cover glass, each light deflecting member comprising atransparent body having three sides, one of which is contiguous with theinner face of the cover glass While the other two sides converge to forma ridge which lies along a chord of the curve dening the concave face ofthe cover glass, the ridges of the light deflecting members beingparallel and one of the converging sides of each light deflecting memberbeing an active face and cylindrical, the active faces of the lightdeflecting members being on the same sides of the ridges.

3. The combination with a cover glass having a convex outer face and aconcave inner face of a plurality of light deecting members on the innerface of the cover glass, each light deflecting member comprising atransparent body having three sides, one of which is contiguous with theinner face of the cover glass while the other two sides converge andform a ridge which lies along a line which intersects two spaced pointson the concave face of the cover glass, the ridges of the lightdeflecting members being parallel, one of said converging sides of eachlight deflecting member being an active face of concave cylindrlcalcontour as it recedes from the ridge, the active faces of the lightdeflecting members being on the said sides of the ridges.

4. The combination with a cover glass having a convex outer face and aconcave inner face of a plurality of light deflecting members on theinner face of the cover glass, each light deflecting member comprising atransparent body having three sides, one of which'is contiguous with theinner face of the cover glass while the other two sides converge to forma ridge which lies along a chord of the curve defining the concave faceof the cover glass, the ridges of the light deflecting members beingparallel and one of the converging sides of each light deecting memberbeing of concave cylindrical contour. the active faces of the lightdeflecting members being on the same sides of the ridges.

STATES LEE LEBBY.

